Research attempts to prevent excess gestational weight gain, defined as gaining more weight during pregnancy than Institute of Medicine (IOM) guidelines for prepregnancy body mass index (BMI), have largely been unsuccessful. Roughly 62% of overweight and 45% of obese women still gain more weight than recommended, increasing risk for postpartum weight retention. Few mobile health (mHealth) interventions have been trialed to address pregnancy-associated weight gain, which is a missed opportunity. Adult women are high users of technology for general and pregnancy-specific health information seeking and sharing. To fill this gap, our long-term goal is to disseminate into clinical practice a standalone mHealth tool that is effective for overweight and obese pregnant women to achieve gestational weight gain within IOM recommendations and return to prepregnancy weight after childbirth. The goal of this application is to test GROWell: Goals for Reaching Optimal Wellness, an innovative, mHealth tool based on Self-regulation Theory that we designed in pilot work to achieve appropriate gestational weight gain and safe postpartum weight loss. We propose a blinded randomized controlled trial to test the efficacy of GROWell compared to an attention control also developed in our pilot. We will recruit 480 women ages 18-44 with prepregnancy BMI 25-<40 and 10-16 weeks gestation of a singleton, uncomplicated pregnancy. Block randomization based on BMI, race, and recruitment clinic will be used to assign participants equally to arm 1, GROWell (n=240), or arm 2, the attention control (n=240). Upon study enrollment and through 6 months postpartum, GROWell participants will receive daily text messages that provide tailored education, problem-solving skills, and support to aid their personalized dietary goals. Once weekly, participants self-monitor overall adherence to their goals using text messages that prompt them to report on how they did in the past week. When users respond to this prompt, they immediately receive a text with tailored feedback on their adherence and long-term progress toward their goals. Control participants will receive weekly texts that provide personalized self-care, pregnancy, labor, delivery, and early infancy education. The specific aims are to: (1) Compare the efficacy of GROWell to the attention control in reducing the proportion of women who gain excess gestational weight based on IOM guidelines (>25 lbs for overweight and >20 lbs for obese) controlling for demographics, parity, physical activity, diet quality, and depression/anxiety; and (2) Compare the efficacy of GROWell to the attention control in reducing postpartum weight retention at 6 months post-birth as measured by the proportion of women who are within 5% of their prepregnancy weight, controlling for demographics, parity, physical activity, diet quality, breastfeeding, and depression/anxiety. This research addresses PA 18-135 (Maternal Nutrition and Pre-pregnancy Obesity) and will provide an innovative, evidence-based, standalone mHealth tool to reduce excess gestational weight gain and postpartum weight retention among overweight and obese women, currently an unavailable resource.